High temperature structural material and method of producing same



United States Patent HIGH TEMPERATURE STRUCTURAL MATERIAL AND METHOD OF PRODUCING SAME John S. Nachtman, Washington, D. C.

No Drawing. Application January 4, 1955 Serial N0. 479,874

8 Claims. (Cl. 29-1825) (Granted under Title 35, U. 8, Code (1952), sec. 266) of producing structural materials therefrom by utilization i of certain techniques of powder metallurgy.

In the prior art, metal oxides, inorganic compounds of mixed metal oxides, and other inorganic non-metallics are usually considered to be detrimental to the useful properties of base metals or metal alloys containing such substances in substantial percentage. This, however, is 'not' always true, and contrary to prior teachings it has been found that the proper amount anddistribution 'of these substances lead to enhanced properties in metals and alloys.

For example, structural materials possessing unusual and desirable properties may be produced by powder.

metallurgical processes from compositions of aluminum or aluminum alloy powder containing finely dividedin-fl organic additives of substances other than aluminum oxide alone, such as metal oxides, compounds of mixed metal oxides, and other inorganics, both metallicandi non-metallic. The structural material produced therefrom and in accordance with this invention are characa terized by relatively light weight and greatly improved strength and hardness at elevated temperatures up 'to' about 1200 F.

It is a principal object of thisinvention to produce compact substantially non-porous aluminum base structural material possessing light weight and greatly improved hardness and strength at temperatures up to about 1200 F.

It is another object of the invention to produce compact substantially nonporous light weight structural materials characterized by'unusual strength .andhardness at elevated temperatures from compositions comprising aluminum or aluminum alloy powderandfinel'y divided of two or more of the foregoingsubstances.

2,840,891 Patented July 1, 1958 inorganic additives of substances other than aluminum oxide alone. V 7.

It is a further object of the invention to provide methods of producing such compact substantially nonporous structural materials from the before mentioned powder compositions by utilization of suitable powder metallurgical techniques; a

Still further objects of the'invention include compact substantially non-porous structural materials, and forms therefrom, resulting from such powder compositions and methods. e

Still further objects and the attendant advantag ing from the spirit and 'scope of the invention.

Broadly stated, the foregoing objects may be accom plished by means of a process comprising the'following steps: (1) producing a'powder composition comprising; aluminum or aluminum ,alloy powder and a suitable' finely divided inorganic additive; (2) milling said powder composition preferably with sufficient wetting a'gent to, 'form a soft paste; (3) preferably presintering the milled; powder composition at about 800 F underian'inert atmosphere, and then cooling to room temperature before? exposing to air; (4) utilizing techniques of powder metal- 1 lurgy to produce a desired form from the before mentioned powder composition.

The process, as briefly set forth; above, is hereinafter described with particular reference to producing compacts" from a powder composition consisting of approximately -95 parts aluminum powder and approximatelyS-SO parts titanium dioxide. However, it will be appreciated that the invention is not; limited to such compositions or;

the production of such compacts, and that other well known powder metallurgical techniques may be used to, form larger or more complicated shapes from thepowderj composition resulting from steps (1) through (3).

Regardless of the final form, the structural materialj produced in accordance with the invention is sh m-j terized by light weight, compact relatively-nonporous forms of unusually high strength and hardnessatceler-j vated temperatures up to about 1200 F. -as" di stiI i Q guished from'conventional porous ceramics which have;

low physical strength.

Table I gave hardness data 'for various'stages'in ithei processing of compacts and hot hardness data at different testing temperatures. Examples are'given therein: of

compacts composedof aluminum powder, aluminum pow! der and a metal :oxide, aluminum powder and'a com pound of mixed metal oxides, aluminum powder and a metal, aluminumpowder and either a metal sulfide, carbide, boride, or oxygen bearing compounds and mixturesa es of the invention will be obvious to those skilled'in the mi from the more detailed description set forth belowgit, being understood that the following detailed'descriptiong is given by way of illustration and explanation only,nand'-" not by way of limitation, since various changes therein: may be made by those skilled in the art without depart-f TABLE L-HOT HARDNESS OF ALUMINUM BASE POWDER PRODUCTS Percent Additive to Aluminum Powder Rockwell superitlcial hardness number, Rw 04; dia. steel ball-15 kgm. load) Individual Total Rw as Rw Sin- Rw Rw Rw Rw Rw Rw Pressed tered Colned 1,000 F. 1,10o F. 1,15o F. 1,200 F. 1.250 13.

Pure Aluminum 88 89 93 66 50 23 T10 88 90 67 56 28 off scale 87 90 90 70 55 36 10 .5 92 92 73 54 22 50 84 90 90 77 s2 s2 79 72 5 s7 s4 s9 67 60 45 5 87 s4 s9 63 48 28 10 s7 s1 88 62 55 36 25 59 69 87 57 62 52 40 5 as 87 88 59 50 35 10 s5 s5 s9 67 4s 42 H 25 s5 s5 82 as 52 30 26 5 85 86 88 55 45 25 .25 s5 s5 s7 55 48 51 47 5 86 83 87 67 53 45 ofl scale 10 s5 s4 88 66 53 3o 26- 25 s7 s5 88 70 59 as 42 5 85 d 10 84 on scale 25 84 30 5 ss 10 88 25 s3 5 s5 5 s5 10 e5 25 e4 5 s4 10 84 5 81 5 s4 10 88 25 83 5 s4 10 84 25 86 5 as 10 89 5 s7 10 82 25 so 5 s7 10 85 25 85 10 88 25 87 e 5 s1 s5 s2 72 as on scale 1o 87 88 so 54 50 25 ofi scale l V 25 s9 s9 90 74 '55 44 .W, 50 85 88 s9 85 so 79 74 76 10 87 r 90 a4 10 89 88 91 as 5 1 27 ss 39 a4 5 s5 41 1o s5 47 25 ss l 5 s4 43 1o s5 45 12.5% TiOz 25 53 It is apparent from Table I that many diiferentiino'rbe highly efiective are titanium dioxide, a titanium dioxganic substances may be added to aluminumpowder to inide-aluminum oxide mixture, magnesium oxide,v chromic crease hardness and strength at elevated temperatures of oxide, praseodymium oxide, and molybdenum, sesquioxproducts made from the composite powder. Metal OX- ide. 7 r ide additives and mixtures thereof have generally proven -The simple metal oxide additives found tobe useful to be very effective in retaining hardness and strength for the purpose of this invention are those inorganic oxin aluminum for most purposes. These oxides found to ides of metals other than aluminum which? are stable and not appreciably reactive with aluminum or oxygenat temperatures up toabout 1200 F., and mixtures of one or more of such oxides with or Without aluminum oxide.

The compounds of mixed oxides useful as additives to aluminum or aluminum alloy powder for the purpose of the invention may be defined as those inorganic comopnds of mixed oxides'which are stable and not appreciably reactive with aluminum or oxygen at temperatures up to about 1200 F., and mixtures of one or more of such mixed oxides. An, example of one such compound is calcium titanate, CaTiO which may be considered as a compound of calcium oxide and titanium dioxide, CaO-TiO for the purposes of the invention. Other examples are aluminates, titanate, silicates, and analogous compounds of vanadium, chromium and nickel.

The metal powders useful as additives to aluminum powder compositions in accordance with the invention are metals known in the art as strengthening metals for aluminum alloys. Examples of such metals are Fe,,Mo, V, Ti, Ta, Cb, Cr, Mn, Ni, W, B, and rare earth elements.

It is understood that mixtures comprising one or more of the before mentioned metals, simple metal oxides, or mixed metal oxides are useful as additives, as well as metal sulfides, carbides, borides, and inorganic oxygen bearing compounds which do not decompose or react appreciably with aluminum or oxygen at temperatures up to about 1200 F.

In order to obtain the improvement in properties of aluminum based powder products described herein, it appears desirable that the fine aluminum particles be uniformly surrounded by non-reactive heat-stable inorganic barriers to the diffusion of aluminum atoms. Additives which decompose upon heating or react appreciably with aluminum or oxygen at temperatures up to about 1200" F. reduce hot hardness and strength, and in some instances destroy the completed product as a result of the reaction.

The most satisfactory aluminum powder for use in powder compositions of the invention is very finely divided 1% retained on 325 mesh screen) low lubricant flake aluminum powder. It is also highly desirable that additives thereto be in a finely divided state. An additive particle size of 5-50 microns was found to be suitable, but no particular correlation was found between particle size and hardness. However, all satisfactory additives. were quite fine powders, as shown'by Table II.

Table II gives the Rockwell hardness value (Rw) at 1120 F. and compressive strength (CS) in pounds per 7 square inch at 70 F. for aluminum base powder products composed of low lubricant flake aluminum powder (1% retained on 325 mesh screen) and additives in percentages by weight having various particles sizes in microns (u). The Rockwell hardness values (Rw) for Table II, as well as Table I, were obtained by following the testing procedure to be described in the example.

The compressive strength (CS) was obtained by inserting experimental data in the formula CS=P/A and making computations therefrom, where P is the maximum lead before failure in pounds and A is the cross-sectional area of the aluminum base powder product in square inches.

The following specific example of the invention for preparing a metallurgical powder composition and manufacture of a form therefrom is given for purposes of illustration only:

Example PREPAJRATION OF POWDER A dry powder composition was prepared from 50% (by weight) low lubricant flake aluminum powder 1% retained on 325 mesh screen) and 50% finely divided titanium dioxide (average particle size 501.4).

In order to press the powder composition it was found desirable to ball mill (mill capacity 1000 cc., containing 165% and 140% steel balls, speed of rotation 96 R. P. M.) a 40 gm. powder charge with sufiicient wetting agent (xylene) to form a soft paste (25-60 cc.).

The milled charge was removed from the ball mill, separated from the steel balls, then placed in an aluminum boat and pre-sintered for one hour at 800 F. under inert (argon) atmosphere. The charge was cooled to room temperature before exposing to air.

MANUFACTURE AND PROCESSING OF .COMPACTS The powder composition as above prepared was'found to be readily pressed. A compact was made using a double action die and a pressure of 40 tons p. s. i. Pres- TABLE II. PARTICLE SIZE OF ADDITIONS, HARDNESS 1120 F. AND CQMPRESSIVE STRENGTH OF ALUMINUM BASE POWDER PRODUCTS Hardness 1,120 E. Compressive Strength 70 F.

' a Size Avg. 5% Addition 10% Addition 25% Addition 50% Addition Addition Rim; Sage O. 8., O. 8., C. S., 0. SI, Rw p. s. i. X Rw p. s. i; X Rw p. s. i. X Rw p. s. i. X

5 53 49.8 25 37 52. 6 29 53. 3 7:5 46 52. 8 57 49. 2 5g 30 57. 0 35 53. 6 12.5 25 53.4 p 36 51.4 12. 5 34 51. 9 45 49. 2 1.25 j 49 51.5 g 50 53.2 2. 5 42 53. 4 44 53.8 12. 5 25 52. 4 25 50.9 12.5 36 54. 3 12.5 36 56. 4 5 46 50. 2 46 54.6 12. 5 42 53. 3 48 51. 5

1 sures greater than this caused welding of the-aluminum to the walls of the'die and eventually resulted in fracturing of the die, as well as cracking of the specimen upon ejection from the die.

A sintering step was carried out at 1000-1050 'F. for one hour under inert (argon) atmosphere, followed by air cooling to room temperature.

It was found that compacts harder at room temperature were also harder at elevated temperatures. Accordingly, all compacts were repressed after sintering by a process known as coining, and in the same die used for making the compacts.

It was noted in most instances that due to cold welding, the pressed compacts were about as hard as after complete processing. Where cold welding is achieved during the pressing step, it appears that the sintering step may be omitted in some instances.

TESTING OF COMPACTS Hot hardness testing of the products as above prepared was chosen because of the well known correlation between hot hardness, creep, and creep-rupture strength. Compacts prepared in accordance with the invention, as previously described, were hot tested using a Rockwell Superficial Hardness tester with a 15 kg. load and A steel ball ind-enter (Rockwell w scale). The anvils were cylindrical stainless steel blocks 3 in height and 2 /2 in diameter with cylindrical cavities in the top. A larger anvil was used to support the stainless steel block with a. A" sheet of transite interposed between the larger anvil and stainless steel block.

The stainless steel blocks were heated to testing temperature and a compact specimen placed in the cavity. The assembly was furnace-heated to testing temperature and the temperature maintained for a period of one hour. The assembly was then removed from the furnace to the Rockwell Superficial Hardness tester and readings (Rockwell w scale) taken as rapidly as possible.

It is to be understood that the invention is not limited to aluminum or aluminum alloy powder as the basic metallic component of the described metallurgical powder compositions, or tothe preparation of such powder compositions by the described addition of powdered additives. Aluminum powder or other metallic powder, or aluminum flake or other metallic flake, and mixtures thereof may be either admixed or coated with metal additive or other inorganic additive described hereinto produce the metallurgical powder compositions of the invention. Alternatively, the basic metallic component of powder compositions may be coated with inorganic additive by any suitmay be processed into a body of desircd size andshape by ,sisting of iron, molybdenum, vanadium, titanium, tantalum, columbium, chromium, manganese, nickel, tungsten, boron and the rare earth elements, mixtures of said compounds with aluminum oxide, and mixtures of said compounds with said strengthening metals and aluminum oxide, said inorganic oxygen bearing compound comprising at least 5 parts by weight of said composition.

2. The metallurgical composition of claim 1 wherein the inorganic oxygen bearing compound is a compound of titanium.

3. The metallurgical composition of claim 1 wherein the additive contains aluminum oxide.

4. A structural material formed by mechanical working under pressure from a finely divided mixture of 75 to 95 parts by weight of a metallic base selected from the group consisting of aluminum and alloys of aluminum and 25 to 5 parts by weight of an additive selected from the group consisting of the inorganic oxygen bearing compounds of a metal selected from the group consisting of magnesium, titanium, vanadium, chromium, zirconium, lanthanum, cerium and praseodymium, which compounds do not contain any non-metal other than oxygen, mixtures of said compounds, mixtures of said compounds with aluminum alloy strengthening metal-s selected from the group consisting of iron, molybdenum, vanadium, titanium, tantalum, columbium, chromium, manganese, nickel, tungsten, boron and the rare earth elements, and mixtures of said compounds with aluminum oxide, said inorganic oxygen bearing compound comprising at least 5 parts by weight of said composition, said finely divided mixture having been heated under non-oxidizing conditions to a temperature between about 800 F. and about the-melting point of aluminum.

5. A structural material formed by mechanical working under pressure from a finely divided mixture of 75 to. 95 parts by weight of a metallic base selected from the do not contain any non-metal other than oxygen, mixtures the described method or by'other suitable well known H present invention are possible in the light'of the above.

teachings. It is, therefore, to be understood that within the scope of the appended claims the; invention may be practiced otherwise than as specifically described.

, What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A metallurgical composition for use in the production of structural material capable of unusual strength.

and hardness upto about 1200 F. comprising an intimate finely divided mixture consisting of 75 to 95 parts by, weight of a metallic base selected frorn the group con' sisting of aluminum and alloys of aluminum, and "25 to 5 of said compounds, mixtures of said compounds with aluminum alloy strengthening metals selected from the group consisting of iron, molybdenum, vanadium, titanium, tantalum, columbium, chromium, manganese nickel, tungsten, boron and the rare earth elements, and mixtures of said compounds with aluminum oxide, said inorganic oxygen bearing compounds comprising at least 5 parts by weight of said composition, said finely divided mixture having been heated under non-oxidizing conditions to a temperature between about 800 F. and about the melting point of aluminum.

6. The structural material of claim 5 wherein the in organic oxygen bearing compound is a compound of titanium. V

7. The structural material of claim 5 wherein the additive contains aluminum oxide. 7

8. The method of producing a structural material capable of unusual strength and hardness up to about 1200 F. by heating under non-oxidizing conditions to a temperature from about 800 F. to about the melting point of aluminum a finely divided mixture of 75 to 95 parts by weight of a metallic base, selected from the group consi'stingof aluminum and alloys of aluminum and 25 to 5 parts by weight of an additive selected from the group consisting of the inorganic oxygen bearing compounds of a metal selected from the group consisting of magnesium, titanium, vanadium, chromium, zirconium, lanthanum, cerium and praseodymium, which compounds do not contain any non-metals other than oxygen, mixtures of said compounds, mixtures of said compounds with aluminum alloy strengthening metals selected from the group consisting of iron, molybdenum, vanadium, titanium, tantalum, columbium, chromium, manganese, nickel, tungsten, boron and the rare earth elements, mixtures of said compounds with said strengthening metals and mixtures of said compounds with aluminum oxide, said inorganic oxygen bearing compound comprising at least 5 parts by weight of said composition, and mechanically working said mixture under pressure to form said material.

References Cited in the file of this patent UNITED STATES PATENTS Lepp Sept. 18, 1951 Stafford Oct. 7, 1952 FOREIGN PATENTS Great Britain Feb. 8, 1940 France Feb. 18, 1946 Great Britain June 27, 1949 Canada Feb. 10, 1953 Austria Sept. 10, 1953 OTHER REFERENCES Metal Powder Report, vol. 4, No. 8, April 1950,

page 126.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2840,891 July 1, 1958 John 5. Nachtmen It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8 line 6, for "oxygen mixtures" read oxygen, mixtures Signed ald sealed this 9th day of December 1958.

SEAL) ttest: KARL H. AXLINI ROBERT C. WATSON Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,840,891 July 1, l958 J 01 11 S Naehtman It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 6, for "oxygen mixtures" read oxygen, mixtures Signed and sealed this 9th day of December 1958.

SEAL) ttest:

KARL H. AXLINB ROBERT C. WATSON Attesting Oflicer Commissioner of Patents 

1. A METALLURGICAL COMPOSITION FOR USE IN THE PRODUCTION OF STRUCTURAL MATERIAL CAPABLE OF UNUSUAL STRENGTH AND HARDNESS UP TO ABOUT 1200*F. COMPRISING AN INTIMATE FINELY DIVIDED MIXTURE CONSISTING OF 75 TO 95 PARTS BY WEIGHT OF A METALLIC BASE SELECTED FROM THE GROUP CONSISTING OF ALUMINUM AND ALLOYS OF ALUMINUM, AND 25 TO 5 PARTS BY WEIGHT OF AN ADDITIVE SELECTED FROM THE GROUP CONSISTING OF THE INORGANIC OXYGEN BEARING COMPOUNDS OF A METAL SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM, TITANIUM, VANADIUM, CHROMIUM, ZIRCONIUM, LANTHANUM, CERIUM AND PRASEODYMIUM, WHICH COMOUNDS DO NOT CONTAIN ANY NON-METAL OTHER THAN OXYGEN MIXTURES OF SAID COMPOUNDS, MIXTURES OF SAID COMOUNDS WITH ALUMINUM ALLOY STRENGTHENING METALS SELECTED FROM THE GROUP CONSISTING OF IRON, MOLYBDENUM, VANADIUM, TITANIUM, TANTALUM, COLUMBIUM, CHROMIUM, MANGANESE, NICKEL, TUNGSTEN, BORON AND THE RARE EARTH ELEMENTS, MIXTURES OF SAID COMPOUNDS WITH ALUMINUM OXIDE, AND MIXTURES OF SAID COMPOUNDS WITH SAID STRENGTHENING METALS AND ALUMINUM OXIDE, SAID INORGANIC OXYGEN BEARING COMPOUND COMPRISING AT LEAST 5 PARTS BY WEIGHT OF SAID COMPOSITION. 